An important consideration in the commercial electroplating of bright nickel at the present time and for the forseeable future is minimizing the cost of depositing nickel and conserving the nickel metal itself, which is not an unlimited resource, and often in short supply or available only at high cost. To conserve nickel and reduce costs a number of procedures have been tried by the nickel plating industry. One of the earliest approaches to the problem was to reduce the thickness of nickel deposited. However, in order to retain the degree of brightening and leveling to which the nickel plating industry has grown accustomed, it is necessary to use more effective or "powerful" nickel brighteners or higher concentrations of nickel brighteners, so that a bright and well-leveled nickel deposit might be obtained with the thinner deposits. The more "powerful" nickel brighteners or high concentrations of brighteners, while capable of producing the desired brightening and leveling, may nevertheless cause unacceptable side effects. The nickel deposits may be highly stressed, severely embrittled, less receptive to subsequent chromium deposits or exhibit hazes, reduced low current density covering power or "throw" or striations and skip plate, i.e., areas in which a deposit is not obtained.
Another method of saving nickel has been to substitute cobalt for some portion of the nickel, and thereby deposit nickel-cobalt alloys. Generally, cobalt is more expensive than nickel, but at times cobalt may be more readily available than nickel. If thinner deposits of nickel-cobalt alloys are then deposited in order to reduce costs, but higher concentrations of brighteners, or more "powerful" brighteners are employed in the plating bath to retain the desired degree of brightening and leveling, the same problems mentioned previously with respect to nickel plating may become manifest; that is, the deposits may be highly stressed, severely embrittled, hazy, striated, etc.
More recently, electrodeposited alloys of nickel-iron, nickel-cobalt-iron or cobalt-iron have begun to be used commercially as substitutes for decorative nickel electrodeposits in periods when nickel has been in short supply or to reduce the cost of nickel electrodeposits by substituting relatively inexpensive iron for a portion of the more expensive nickel and/or cobalt. Electrodeposited alloys containing as much as 60% by weight iron (with the remainder predominantly nickel and/or cobalt) are thus being used commercially in applications where formerly all nickel electrodeposits were considered necessary.
Although in many respects, the electrodeposition of nickel-iron, cobalt-iron or nickel-cobalt-iron alloys is very similar to the electrodeposition of nickel in that similar equipment, operating conditions and organic additives are employed; nevertheless, electroplating with iron containing alloys of nickels and/or cobalt presents some special problems. For example, in order to maintain the desired ratio of nickel or cobalt ions to iron ions in the electroplating solution, a portion of the nickel or cobalt anodes are desirably replaced with iron anodes to provide ferrous ions to the plating solution as a replenishment for the iron plated out of the bath. These iron anodes should corrode evenly, smoothly and efficiently to avoid anode polarization, as well as to preclude the sloughing off of particles of the iron anodes thereby clogging anode bags and filters or causing rough deposits. Since the introduction of undesirable foreign materials to a plating bath must always be guarded against, the iron anodes should be of high purity. Unfortunately, iron of suitable purity for use as anodes in an iron alloy bath may not corrode evenly in the bath and can result in the aforementioned problems.
Another requirement in the electrodeposition of iron alloys of nickel and/or cobalt is that the iron in the electroplating solution should be predominantly in the ferrous state rather than the ferric. At a pH of about 3.5, basic ferric salts precipitate and can clog the anode bags and filters and may produce rough electrodeposits. It is, therefore, advantageous to prevent any ferric basic salts from precipitating. This can be accomplished by the addition of suitable complexing, chelating, anti-oxidant or reducing agents to the iron containing electroplating alloy bath as taught by Koretzky in U.S. Pat. No. 3,354,059; Passal in U.S. Pat. No. 3,804,726; or Clauss et al. in U.S. Pat. No. 3,806,429. While these complexing or chelating agents are necessary in order to provide a solution to the ferric iron problem, their use may result in several undesirable side effects. They can cause a reduction in deposit leveling and can also produce striated, hazy or dull deposits which may further exhibit step plate or even skip plate, i.e., areas which are not plated, or else plated only very thinly compared to other sections of the deposits.